Not defending the ISP's here, but that's not quite how it works in most of the U.S. In most places, it's labeled Sale Price + sales tax. Sales tax is usually predictable based on City/State, but varies amongst them.
Again, not defending the ISP's here, but at most U.S. stores they like to advertise (for example) "$6 pairs of socks for $9.99+tax." The final price, including tax, will vary by City/State. The "+Tax" part is usually fairly simple because it's just one or two percentage-based summed taxes.
ISP's are trying to do the same thing, except instead of just adding the total local/state/fed tax, they're also adding fees such as maybe Pole fees, billing fees, who knows what else. This allows them to advertise "$49.99/mo for 1Gb service" but once all the fees are added up, it's more like $65mo. Not sure what the right answer here is, but what they should have to do is advertise "$49.99/mo+TaxesAndFees for 1GB service" and then publish what those itemized taxes and fees are for all services areas. They don't want to do the latter.